Jeroen van Bemmel wrote:
>> This way, when A gets the Refer-To [EMAIL PROTECTED], it would just send
>> its subsequent INVITE to the proxy resposible for whatever.com which will
>> then forward it to C.
>>
>> Furthermore, I would've thought that using the addr-of record is always
>> the
>> safer option as it would always get resolved and forwarded to the right
>> place
>> eventually. Is this not true?
>
> No, because it is not guaranteed that [EMAIL PROTECTED] routes to the UA
> instance that C was using in the call with B. It may end up at some other
> device, or e.g. go to voice mail
A slight modification to the original example shows this:
- phoneA.whatever.com calls [EMAIL PROTECTED]
and reaches phoneB.whatever.com
- phoneB.example.com calls [EMAIL PROTECTED],
routed to phoneD.whatever.com
- phoneD is busy. Call is forward-on-busy to [EMAIL PROTECTED],
and reaches phoneC.whatever.com
- phoneD ceases being busy
- phoneB initiates a transfer to connect its two calls.
The contact of the transfer target is phoneC.whatever.com,
and the AOR known to B is [EMAIL PROTECTED]
If B uses the AOR it knows ([EMAIL PROTECTED]) in the Refer-To, then the
transfer will fail, because it will not reach phoneC.example.com. If B
uses the contact address it knows (phoneC.whatever.com) and it is
routable from A, then the transfer will succeed.
This is why GRUU is important - so that C can have a globally routable
contact.
Paul
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